Isobutane Alkylation with Butenes and the Oligomerization of C4 Olefins in Supercritical Reagents

Abstract

The competing reactions of isobutane alkylation with butenes and butene oligomerization under supercritical and ordinary gas-liquid conditions are studied over a variety of catalysts: sulfated zirconia, titania-supported heteropolyacids and tungstia, and chlorinated aluminum-platinum catalyst. Both reactions proceed rapidly, showing no substantial decrease in catalytic activity, under supercritical conditions at 140–165° C and 40–45 atm. By contrast, alkylation and oligomerization in the liquid phase and particularly in the gas phase are accompanied by a rapid deactivation of the catalyst. Passing from ordinary gas-liquid conditions to supercritical conditions dramatically accelerates the reaction and the regeneration of the deactivated catalyst. Reaction selectivity depends significantly on the isobutane/olefins (butenes) (I/Ol) ratio in the initial mixture. At I/Ol = 14, isobutane alkylation with butenes is the main reaction pathway, which results in the complete conversion of the butenes to C8 alkylation products. The yield of saturated isoalkanes is as high as 70%. Reducing the I/Ol ratio to 0.5 results in the domination of butenes over alkylation.